1. Field of the Invention
The present invention relates to phosphorus compounds and methods for preparing the same, and more particularly, to a phosphorous compound with high solubility and a method for preparing the same.
2. Description of Related Art
In order to meet the demand for thin circuits and high density, laminates need excellent electrical property, mechanical performance and particularly resistance to thermal processing. As to a common FR4 laminate, its glass transition temperature is approximately 130° C. after curing. During fabrication of printed circuit boards, laminates have cracking or a popcorn effect due to the processes of stripping and drilling over 200° C., or even welding processes over 270° C. Thus, there are developments on various types of laminate materials with high thermal stability and high glass transition temperatures. In addition, laminates have a further important property, flame resistance, which is advantageous to applications of laminates in some fields, for examples, transportation vehicles like planes, automobiles and public transportation vehicles. Hence, flame resistance of printed circuit boards is absolutely essential.
To increase flame resistance of laminate materials, certain substances having the property of insulating flame to reduce burning are used. As to laminates, halogen compounds, especially bromide-containing epoxy resins and curing agents, are used conventionally with flame retardants such as antimony trioxide to meet the requirement of flame resistance (e.g., UL 94V-0 level). Generally, an epoxy resin must have up to 17-21% bromide, and be used with antimony trioxide or other flame retardants to pass UL 94V-0. However, use of bromide-containing epoxy resins or antimony trioxide undoubtedly has adverse effects on human health, because antimony trioxide is reported as a carcinogenic compound. Further, during burning, bromide generates corrosive bromine radicals and hydrogen bromide, and high concentrations of aromatic compounds in bromide also generate highly toxic bromofurans and bromodioxins, thereby severely affecting human health and the environment.
Currently, the use of phosphorous compounds as the next generation of environmentally friendly flame retardant has been widely investigated and applied. For example, a flame-resistant epoxy resin composition formed from a phosphorus compound disclosed in Taiwanese Patent No. 575633 passes UL 94V-0, and does not release corrosive and highly toxic gases upon heating. However, phosphorus compounds, due to their own structures, are nearly insoluble in solvents commonly applied to epoxy resin compositions, and it is soluble only in solvents with higher polarity. Consequently, solvents with higher polarity are necessary if phosphorous compounds are to be used, thereby causing inconvenience in processing or application.
Accordingly, there still exists a need for a flame-resistant additive with high solubility and a high pyrolysis temperature, which is capable of being applied to thermosetting or thermoplastic resins.